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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
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You just didn't read carefully: the sum of all the waiting times of the customers. And then it is explained clearly in the note.
You must accumulate all the waiting times: The first customer waits 5 minutes and the second waits 27 minutes. All this is in the description, please read it carefully, I'm not even sure I should answer you, I'm giving away the solution...
First customer is waiting 5 minutes, second is waiting 5 (of first customer) + 2(maintanance) + 20(his own waiting time).
So accumulated time is 1 customer time(5) + 2 customer time(27) = 32
You must accumulate all the waiting times.